Summary Gastrointestinal (GI) parasitic nematodes sicken and debilitate billions of people on the planet and have a profound negative impact upon agriculture. Clearly, there is a great need for anti-nematode vaccines, but understanding how these worms are targeted and killed by the immune system has been hampered by difficulties in tracking nematode antigen-specific T cells. Nematodes are protected by a semi-permeable cuticle that limits antigenic exposure prior to their potential degradation within host tissue, making identification of specific requirements for antigen-specific host immunity difficult at present, but nevertheless a high priority for human health. The purpose of this R21 application is to capitalize upon a major technological advance in heritable transgenesis in parasitic nematodes to explore the mechanistic requirements of host protective T cell epitopes. We will use an arsenal of tissue-specific promoters and constructs that can generate both secreted and membrane bound proteins expressing this epitope, we will delineate the requirements for protective CD4+ T cell responses. We will use existing and newly generated transgenic nematode lines combined with MHC II tetramers, cytokine assays, adoptive transfer experiments to address questions in the field of helminth immunology that have not been previously possible. The central hypothesis tested in this project is that secretion and/or membrane localization of model antigens in parasite cells in direct contact with the host environment impacts the identity and protective efficacy of the nematode-specific CD4+ T cell response. Successful completion of this work stands to make a paradigm shifting impact on the field of biomedical research on parasitic helminths.